This disclosure relates to a crystalline polymer composition and a crystal nucleating agent.
Thermoplastic polymers such as polyolefins can be readily molded under a variety of conditions to produce articles for a broad range of applications. One method of improving the transparency and mechanical strength of an article molded from a thermoplastic polymer is to improve the crystallinity of the polymer. Crystallization can be promoted by adding a crystal nucleating agent. In addition, it can be advantageous to control the crystal orientation in the polymer to further improve optical and other properties of the molded article. However, the nucleating effect of commercially available crystal nucleating agents is insufficient on some polymers, in particular polyolefins such as those derived from ethylene and other monomers.
The heat resistance and viscoelastic properties of some polymers can be affected by the incorporation of a polyhedral oligomeric silsesquioxane (“POSS”). For example, Haddad et al. reported that a copolymer obtained by copolymerizing a POSS-containing monomer and styrene provided improved heat resistance and viscoelastic properties compared to a styrene homopolymer. (T. S. Haddad et al., Macromolecules, 1996, Vol. 29, p. 7302.) In addition, L. Zheng et al. have reported a copolymer obtained by copolymerizing a POSS-containing monomer and ethylene or propylene. (L. Zheng et al., Macromolecules 2001, Vol. 34, pp. 8034-8039.) Further, Zheng et al. have reported that if the amount of POSS contained in a copolymer is increased, a plurality of POSS moieties can form an aggregated crystal in the form of plate. (L. Zheng et al., Macromolecules 2002, Vol. 35, pp. 2375-2379.) It has also been found that formation of a POSS aggregated crystal can be controlled by binding an alkyl group to Si in POSS. For example, it has been reported that when a monomer having a POSS containing an ethyl, isobutyl or phenyl group bound to Si is copolymerized with other monomer, the POSS does not readily form an aggregated crystal and a copolymer containing very well dispersed POSS is obtained. (B. Seurer et al., Macromol. Chem. Phys. 2008, Vol. 209, p 2040).
There nonetheless remains a need in the art for an improved crystal nucleating agents for use with thermoplastic polymers such as polyolefins. There further remains a need for both polyolefins and polyolefin compositions having improved crystallinity. It would be a still further advantage if the polyolefins and polyolefin compositions have improved crystal orientation, particularly after crystallization by cooling after deformation under melted conditions.